The present invention relates to a method of operating a vehicle electric motor for driving vehicle-mounted driven equipment such as an auxiliary oil pump which supplies a hydraulic pressure of an ATF to a transmission at, for example, an idle stop of an engine, in order to protect a rolling bearing which pivotally supports a rotation shaft of the electric motor.
In an automobile having an AT (Automatic Transmission), as shown in FIG. 3, the rotation of an engine 1 which is an internal combustion engine is usually changed in speed by a transmission 3 via a torque converter 2, and transmitted to driving wheels which are not shown. The transmission 3 uses an ATF (Automatic Transmission Fluid) as a hydraulic pressure for speed change, and lubrication. The ATF is circulatively supplied from a drain 5 to the transmission 3 by a main oil pump 4 which operates with using the rotation of the engine 1 as a driving force. Although illustration is omitted, also the torque converter 2 receives a supply of the ATF as a power transmission medium fluid from the main oil pump 4. In the figure, I1 indicates various kinds of drive information, and P1 indicates a driving power source at an idle stop.
Among such automobiles, there is an automobile which is equipped with an idle stop function of, in idling operation of the engine 1, stopping the engine 1 by an idle stop controller 6, thereby intending to improve the fuel efficiency and conserve the environment. The idle stop controller 6 controls the engine 1 on the basis of various kinds of drive information such as the travel speed of the automobile, the position of a select lever, and an operation on a pedal. At stopping of the automobile due to a stoplight, a traffic jam, or the like, such as the case where a brake pedal is depressed and the automobile is stopped while being gradually decelerated, the engine 1 is stopped.
When it is predicted that traveling is again started, such as the case where the foot gets off the brake pedal, the engine 1 is restarted. When it is predicted that traveling is immediately restarted, such as the case where the automobile is suddenly stopped, or when the burden of restart of the engine 1 is large, such as the case where the temperature of the engine 1 is low, or the remaining battery capacity is small, the engine 1 is not stopped.
When the engine 1 is stopped by the idle stop function during stopping of the automobile, however, the main oil pump 4 is caused not to operate, and the supply of the ATF to the transmission 3 and the like is cut off so that the hydraulic pressure is lowered. In a situation such as that an acceleration pedal is depressed down immediately after the engine 1 is restarted, even when the supply of the ATF is restarted by the main oil pump 4, the hydraulic pressure is not instantly restored. Consequently, there is a case where smooth restart of traveling is disabled because, for example, the engine 1 once enters the idling state and the automobile is then suddenly started by the restored hydraulic pressure.
In order to comply with this, conventionally, the supply of the ATF is performed also by an auxiliary oil pump 8 driven by an electric motor 7, in addition to the main oil pump 4, so that, when the engine 1 is stopped by the idle stop function, the hydraulic pressure can be maintained by the auxiliary oil pump 8. Namely, when the engine 1 is stopped by the idle stop function, the idle stop controller 6 supplies the driving power source to the electric motor 7 to cause the auxiliary oil pump 8 to operate, during a period when the engine 1 is stopped.
Various configurations in which the electric motor 7 and the auxiliary oil pump 8 are integrated with each other to facilitate installing of them into an automobile have been proposed (for example, see Japanese Patent Publication (Kokai) No. HEI9-32738).
The applicant has already proposed an electric pump in which, as shown in FIG. 4, the electric motor 7 and the auxiliary oil pump 8 are integrated with each other, and a rotation shaft 9 that is shared by the electric motor 7 and the auxiliary oil pump 8 is pivotally supported at the both ends by ball bearings 10, 11 (see Japanese Patent Application No. 2003-23524 “Electric internal gear pump”). In the electric motor 7 of the electric pump, permanent magnets 7a are placed in the rotor, and coils 7c are wound around a core 7b of the stator. The motor is used as a sensorless motor. As the auxiliary oil pump 8, a trochoid pump is used in which an inner rotor 8b having an external gear meshes with the inner peripheral side of an outer rotor 8a having an internal gear, and the rotors 8a, 8b are placed eccentrically and rotatably.
In the case where the above-described electric pump is used as the electric motor 7 and auxiliary oil pump 8 having the idle stop function shown in FIG. 3, only when the automobile is stopped, the electric motor 7 is rotated by the idle stop controller 6, and, during traveling of the automobile, the electric motor 7 is always stopped.
In the ball bearings 10, 11 which pivotally support the rotation shaft 9 of the electric motor 7 and the auxiliary oil pump 8, during a period when the rotation shaft 9 is stopped, however, plural balls 10a, 11a which are rolling elements are stopped on raceway surfaces of outer rings 10b, 11b and inner rings 10c, 11c. When, in this state, repeatedly subjected to vibrations due to traveling of the automobile, the balls 10a, 11a repeatedly collide against the same places of the raceway surfaces, so that impressions are easily formed. In the rotor of the electric motor 7, particularly, the shaft diameter is often increased in order to obtain a larger torque. Since the permanent magnets 7a shown in FIG. 3, and the like are placed, the rotation shaft 9 has a relatively heavy weight. Therefore, impacts which are produced when the balls 10a, 11a receiving vibrations collide against the raceway surfaces are large.
In the case where the rotation shaft 9 of the electric motor 7 used for the idle stop function is pivotally supported by the ball bearings 10, 11, consequently, there is conventionally a problem in that impressions are easily formed on the outer rings 10b, 11b and inner rings 10c, 11c of the ball bearings 10, 11, and the life periods of the bearings are shortened.
The problem is not restricted in the electric pump in which the electric motor 7 and the auxiliary oil pump 8 are integrated with each other, and occurs similarly in the case where the single electric motor 7 is used. The problem is not restricted in the ball bearings 10, 11, and occurs similarly in the case where rolling bearings including various roller bearings are used. Furthermore, the problem is not restricted in the electric motor 7 used for the idle stop function, and occurs commonly in an electric motor for driving driven equipment which is sometimes in no use for a long term during when a vehicle travels.
It is an object of the invention to solve the problem in that, when an electric motor is not rotated for a long term during when a vehicle travels, the life period of a rolling bearing which pivotally supports the rotation shaft of the electric motor is shortened.